onSend feature support for Oulook desktop on-prem

Question

I'm developing an Outlook Web add-in, using Office.js

My target platform is Outlook desktop on-prem: Outlook 2021 (volume-licensed perpetual) + Exchange Server SE

I'd like to perform some actions, when user presses Send button on event creation or update.

I thought, I could use the onSend feature for this,

Outlook 2021 (volume-licensed perpetual) is not being mentioned explicitly in the support matrix of the onSend feature

Theoretically, it should work, as the feature has been introduced in requirements set 1.8 and Outlook 2021 (volume-licensed perpetual) has requirements set support up to 1.9. At least according to the support matrix

I've tried also the official onSend example and it doesn't work in the aforementioned setup
https://github.com/OfficeDev/Outlook-Add-in-On-Send

I didn't find any direct information regarding this on the internet. Only some indirect clues, that most probably it will not work.

Does anybody has any experience with this?

Big thanks in advance!

Answer 1

Hi @aljoscha.s,

Thank you for asking such an important and insightful question about the dependency of the onSend feature on Exchange Server. You are absolutely right in identifying onSend as an Outlook client-side API (Office.js), but the role of the server in enabling it is crucial.

Here’s a detailed explanation of how the server affects this feature and how you can diagnose it:

1. The Role of Exchange Server in the onSend Feature

The onSend feature is not just a local function on the Outlook Desktop client. It is a compliance-driven capability designed to ensure that email content adheres to organizational policies before the message is sent.

2. How to Diagnose onSend Support from Exchange Server

To determine whether your Exchange Server supports and has enabled the onSend feature, an Exchange Administrator needs to perform the following steps:

Diagnostic Method: Check the Mailbox Policy

The most direct way is to inspect the OWA Mailbox Policy applied to the target user’s mailbox using PowerShell in the Exchange Management Shell (EMS):

1. Retrieve the current policy: The administrator should identify which OWA policy is applied to the mailbox.

 

Get-CASMailbox -Identity "<Email Address>" | Select-Object OwaMailboxPolicy

 

1. Check the onSend flag: Once the policy name is known (e.g., OWAOnSendAddinAllUserPolicy), check the status of the onSend flag:

 

Get-OwaMailboxPolicy -Identity "OWAOnSendAddinAllUserPolicy" | Select-Object OnSendAddinsEnabled

 

Diagnostic Results

• If the result is True: This confirms that the Exchange Server has enabled the feature via policy. If the add-in still doesn’t work, the issue likely lies in incompatibility or deployment errors in your Outlook 2021 (perpetual license) or specific Exchange Server SE environment.
• If the result is False: The onSend feature is disabled at the server level. The administrator must enable it using the following command:

 

Set-OwaMailboxPolicy -Identity "OWAOnSendAddinAllUserPolicy" -OnSendAddinsEnabled:$true

 

The onSend feature has a dual dependency: it requires both the Mailbox API 1.8+ on the Outlook client and the OnSendAddinsEnabled flag to be turned on in Exchange Server.

You should coordinate with your Exchange Administration team to perform this check. If the flag is confirmed to be enabled but the feature still fails, it is almost certainly due to incompatibility with perpetual license products in an on-premises environment.

To obtain more accurate information, you may consider visiting the following forum:

Microsoft 365 and Office Development Office JavaScript API - Microsoft Q&A

We apologize for redirecting you to another community, as most members in this category primarily focus on Microsoft 365 users and have limited knowledge about APIs. Therefore, to receive faster and more effective support, allow me to guide you in the right direction.

We are more than happy to assist you, but we’re concerned that providing inaccurate information may not be beneficial to you. We sincerely hope you’ll find the perfect solution with support from experienced experts and community members. We also welcome any community member to share ideas regarding your situation if they have relevant experience.

If you have any updates regarding the issue, or if you have any other questions, please feel free to share them with me. I will support you to the best of my ability.

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Answer 2

Hi @aljoscha.s,

Welcome to the Microsoft Q&A forum.

Thank you for sharing the details of your issue. I’d like to provide you with the following information:

Although Outlook 2021 (volume-licensed perpetual) supports Requirement Set 1.9, the onSend feature has several significant limitations in on-premise environments:

1. Dependency on Exchange Server: The onSend feature requires support from Exchange Server. However, Exchange Server SE may not provide all the necessary API endpoints for full functionality.
2. Outlook Desktop Architecture: Outlook desktop uses a separate webview, which imposes limitations on intercepting system events such as the "Send" button.
3. Microsoft’s Prioritization: New features are typically prioritized for Microsoft 365/Exchange Online before being considered for on-premise environments.

If you’re looking to develop an effective add-in for Outlook, I recommend reaching out to Microsoft’s technical support team via the following link: https://admin.microsoft.com. Once you submit a support request, a live agent will contact you directly through your selected method and assist you step-by-step until your add-in is successfully developed.

If you have any further questions or concerns, feel free to share them with me. I’m here to help.

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